A relief printing plate is a letterpress printing plate having a relief layer with asperities, and such a relief layer with asperities is obtained by patterning a relief-forming layer comprising a photosensitive composition containing as a main component, for example, an elastomeric polymer such as a synthetic rubber, a resin such as a thermoplastic resin, or a mixture of a resin and a plasticizer, thus forming asperities. Among such relief printing plates, one having a soft relief layer is sometimes called a flexographic plate.
As a process for making a plate by directly engraving a relief-forming layer by means of a laser, a direct engraving CTP method is known. The direct engraving CTP method is a method in which relief-forming asperities are formed by engraving by means of a laser itself, and has the advantage that, unlike relief formation using an original image film, the relief shape can be freely controlled. Because of this, when an image such as an outline character is formed, it is possible to engrave that region more deeply than other regions, or in the case of a fine halftone dot image it is possible, taking into consideration resistance to printing pressure, to engrave while adding a shoulder.
Furthermore, International Patent Application WO 2008-133807 describes a composition for laser engraving that comprises a depolymerizable binder polymer.